The goal of this project is to evaluate the toxicity of pentavalent (sodium metavanadate) and tetravalent (vanadyl sulfate) vanadium compounds, following exposure in drinking water. Three-month studies of both compounds are in progress. Humans are likely to be similarly exposed to these compounds in drinking water. These subchronic studies will provide valuable data to design more definitive reproductive/developmental and chronic toxicity/carcinogenicity studies. In addition, these three-month studies were designed similarly to allow comparisons of the toxicity between pentavalent and tetravalent vanadium. Keywords: toxicity, drinking water, vanadium, pentavalent, tetravalent, vanadyl sulfate, sodium metavanadate.